This invention relates to a process of preparing and a process of using a non-pillared metal oxide triple layered perovskite, having a surface area of at least 30 m2/g and the empirical formula
AB2M3O10xe2x88x92x
where A is a monovalent exchangeable cation, B is a divalent or trivalent cation and M is a +2, +3, +4 or +5 valent metal.
Various metal oxides are known as catalysts for numerous chemical reactions. One family of such metal oxides are those having the general formula ABO3 and that have the perovskite structure. Perovskites of course have been known for a number of decades and have been shown to have superconducting, ferromagnetic or ferroelectric properties. In addition to the stoichiometric perovskites, there are oxides that have structures derived from the perovskite structure. One category comprises non-stoichiometric compositions such as ABO3xe2x88x92x where the point defects are ordered in a specific manner to produce perovskite superstructures. Examples of these are Ca2FeAIO5 and YBa2Cu3O7. The second category of perovskite-derivative structures are those that contain two-dimensional perovskite layers of composition Anxe2x88x921BnO3n+1 as one of the units building the layered structure. Another series of layered perovskites has the formula Axe2x80x2[Anxe2x88x921BnO3n+1] where Axe2x80x2 is K, Rb or Cs. One member of this series is Cs Ca2Nb3O10.
The layered perovskite type oxides are interesting because of the potential to carry out chemistry between the layers. References to layered perovskite oxides include: Chem. Mater., 6, 907-912 (1994) which discloses an anion-deficient layered perovskite with a formula of ACa2Nb3xe2x88x92xMxO10xe2x88x92x; J. Mater. Chem. 3(7), 709-713(1993) which discloses layered oxides having a formula of A2xe2x88x92xLa2Ti3xe2x88x92xNbxO10; J. Phys. Chem., 97, 1970-1973 (1993), which discloses a niobate layered perovskite having the formula ALaSrNb2MIIO9.
All of the above described perovskites are prepared by solid state high temperature reaction and consequently have very low surface areas. In order for these perovskite type oxides to have greater widespread utility, it is important to synthesize layered compositions with large surface areas. There are reports of the synthesis of high surface area oxides with the pyrochlore structure. These are: U.S. Pat. No. 5,015,461 which discloses the synthesis of an oxide having the formula A2B2O7 where A is a divalent cation and B is niobium and/or tantalum and has the pyrochlore structure and Mat. Res. Bull., 27, 981-988 (1992) disclosing the synthesis of calcium-niobium and tantalum oxides with the pyrochlore structure and high surface area. Finally, U.S. Pat. No. 4,980,333 discloses a layered perovskite containing interspathic polymeric oxides between the layers. These polymeric oxides prop up the layers thereby increasing its surface area.
In contrast to the above art, applicant has synthesized metal oxide triple layered perovskites having a surface area of at least 30 m2/g and an empirical formula of:
AB2M3O10xe2x88x92x
where A is a monovalent exchangeable cation, B is at least one metal ion having a valence of +2 or +3, M is at least one metal ion having a valence of +2, +3, +4 or +5 and xe2x80x9cxxe2x80x9d has a value from about 0 to about 1. It is also important to note that unlike U.S. Pat. No. 4,980,333, applicant""s perovskites do not contain any pillars or interspathic polymeric oxides between the layers.
As stated the present invention relates to a process for preparing triple layered perovskites and a process for using them. Accordingly one embodiment of the invention is a process for preparing metal oxide triple layered perovskite having a surface area of at least 30 m2/g and an empirical formula of:
AB2M3O10xe2x88x92x
where A is a monovalent exchangeable cation, B is at least one metal ion having a valence of +2 or +3, M is at least one metal ion having a valence of +2, +3, +4 or +5 as defined by the equation:
M3=Me+2+Mf+3+Mg+4+Mh+5
where xe2x80x9cexe2x80x9d, xe2x80x9cfxe2x80x9d, xe2x80x9cgxe2x80x9d and xe2x80x9chxe2x80x9d are the mole fractions of M+2, M+3, M+4 and M+5 respectively, xe2x80x9cexe2x80x9d has a value from about 0 to about 1, xe2x80x9cfxe2x80x9d has a value from about 0 to about 1, xe2x80x9cgxe2x80x9d has a value from about 0 to about 3, xe2x80x9chxe2x80x9d has a value from about 0 to about 3, 3=e+f+g+h and 1xe2x89xa7e+f and xe2x80x9cxxe2x80x9d has a value from about 0 to about 1, the process comprising forming a reaction mixture containing reactive sources of xe2x80x9cAxe2x80x9d, xe2x80x9cBxe2x80x9d and xe2x80x9cMxe2x80x9d at a pH greater than seven, a temperature and a time sufficient to form the perovskite, the reaction mixture having a composition expressed in terms of mole ratios of oxides of
aA2O:bBOy:cMOz:dH2O
where xe2x80x9caxe2x80x9d has a value of about 0.2 to about 2, xe2x80x9cbxe2x80x9d has a value of about 2, xe2x80x9cyxe2x80x9d has a value of about 1.0 to about 1.5, xe2x80x9ccxe2x80x9d has a value of about 3, xe2x80x9czxe2x80x9d has a value of about 1.67 to about 2.5 and xe2x80x9cdxe2x80x9d has a value of about 10 to about 500.
Another embodiment of the invention is a process for removing contaminant ions from a stream comprising contacting the stream with a metal oxide triple layered perovskite at exchange conditions for a time sufficient to exchange the contaminant ion for an exchangeable cation on the perovskite, a surface area of at least 30 m2/g and an empirical formula of:
AB2M3O10xe2x88x92x
where A is a monovalent exchangeable cation, B is at least one metal ion having a valence of +2 or +3, M is at least one metal ion having a valence of +2, +3, +4 or +5 and defined by the equation
M3=Me+2+Mf+3+Mg+4+Mh+5
where e, f, g and h are the mole fractions of M+2, M+3, M+4 and M+5 respectively, xe2x80x9cexe2x80x9d has a value from about 0 to about 1, xe2x80x9cfxe2x80x9d has a value from about 0 to about 1, xe2x80x9cgxe2x80x9d has a value from about 0 to about 3, xe2x80x9chxe2x80x9d has a value from about 0 to about 3, 3=e+f+g+h and 1xe2x89xa7e+f and xe2x80x9cxxe2x80x9d has a value from about 0 to about 1.
These and other objects and embodiments of the invention will become more apparent after the following detailed description of the invention.